1. Field of Invention
The present invention relates to a system and a method of controlling a transmission for a vehicle. More particularly, the present invention relates to a system and a method of controlling a transmission for a vehicle that can protect the transmission by controlling an oil temperature in the transmission when driving on a long uphill road.
2. Description of Related Art
An automatic transmission predicts a driver's will and performs a shift automatically according to the predicted driver's will. A vehicle where the automatic transmission is mounted is provided with a torque converter disposed between an engine and the automatic transmission. The torque converter increases torque of the engine hydraulically and delivers the increased torque to the automatic transmission. Since the torque converter transmits the torque hydraulically, power delivery efficiency may be low.
To solve such problems, the torque converter is provided with the lock-up clutch. The lock-up clutch delivers the torque of the engine to the automatic transmission without torque multiplication by directly coupling the engine to the automatic transmission at a region where power delivery efficiency of the torque converter is poor.
Generally, when the vehicle provided with the automatic transmission runs on an uphill road, the lock-up clutch is released and the vehicle drives using torque multiplication effect of the torque converter for securing drivability. However, if the vehicle drives on a long uphill road, heat energy is excessively generated by hydraulic friction, and thus the oil temperature of the automatic transmission rises to a threshold temperature or higher. At this time, the lock-up clutch is engaged and hydraulic friction is reduced for protecting the automatic transmission.
FIG. 4 shows a conventional method of controlling a transmission when a vehicle provided with an automatic transmission runs on a long uphill road.
As shown in FIG. 4, when the vehicle provided with the automatic transmission enters the long uphill road during running at a seventh forward speed, a controller releases the lock-up clutch and maintains a shift-speed to be the seventh forward speed. In this case, since the lock-up clutch is released, the oil temperature of the automatic transmission rises due to the hydraulic friction.
If the oil temperature of the automatic transmission rises to a threshold temperature or higher, the controller engages the lock-up clutch so as to prevent rise of the oil temperature. Since torque multiplication effect vanishes if the lock-up clutch is engaged, torque transmitted from the engine to the automatic transmission is reduced.
Therefore, the automatic transmission lowers the shift-speed so as to assist the torque. That is, the shift-speed is lowered from the seventh forward speed to a sixth forward speed or a fifth forward speed.
If the conventional method of controlling the transmission is applied, the automatic transmission may be protected to a certain degree but it is difficult to prevent rise of the oil temperature. Since the shift is performed on the uphill road, shift feel may be deteriorated.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.